remove empty nodes

panda/src/pgraph/sceneGraphReducer.cxx

@@ -299,6 +299,19 @@ r_flatten(PandaNode *grandparent_node, PandaNode *parent_node,
         num_nodes += flatten_siblings(parent_node, combine_siblings_bits);
       }
     }
+
+    // Finally, if any of our remaining children are plain PandaNodes
+    // with no children, just remove them.
+    {
+      for (int i = parent_node->get_num_children() - 1; i >= 0; --i) {
+        PandaNode *child_node = parent_node->get_child(i);
+        if (child_node->is_exact_type(PandaNode::get_class_type()) &&
+            child_node->get_num_children() == 0) {
+          parent_node->remove_child(child_node);
+          ++num_nodes;
+        }
+      }
+    }
   }
 
   return num_nodes;